Puromycin dihydrochloride

Puromycin dihydrochloride is a aminonuclease antibiotic that inhibits protein synthesis. Puromycin is used for selection and maintenance of cell lines expressing a transfected pac gene (S. alboniger), whose product, puromycin acetyltransferase, inactivates puromycin via acetylation; recommended concentration in cell culture 1-10µg/ml. Lot-to-lot variations in potency exist for all selection antibiotics, each new lot of puromycin should be titrated. The working puromycin concentration for mammalian cell lines ranges from 1-10 µg/ml. Prior to using the puromycin antibiotic, titrate the selection agent to determine the optimal concentration for target cell line. Use the lowest concentration that kills 100% of non-transfected cells in 3-5 days from the start of puromycin selection.

Depending on individual cell type and doubling rate, selection of stable transfectants will take between 7 and 28 days. Expansion and characterization of single cell clones will take several weeks in addition. Media should be changed out every 2-3 days. This eliminates potentially toxic substances produced by dying cells and secondly, it keeps the concentration of the antibiotic at a constant level.

Factors Influencing Successful Transfection

Transfection in serum-free media – the highest transfection efficiencies can be obtained if the cells are exposed to the transfection complexes in serum free conditions followed by the addition of medium containing twice the amount of normal serum to the complex medium 3–5 hrs post transfection (leaving the complexes on the cells). However, the transfection medium can be replaced with normal growth medium if high toxicity is observed.

No antibiotics in transfection medium – The presence of antibiotics can adversely affect the transfection efficiency and lead to increased toxicity levels in some cell types. It is recommended that these additives be initially excluded until optimized conditions are achieved, then these components can be added, and the cells can be monitored for any changes in the transfection results.

High protein expression levels – Some proteins when expressed at high levels can by cytotoxic; this effect can also be cell line specific.

Cell history, density, and passage number –It is very important to use healthy cells that are regularly passaged and in growth phase. The highest transfection efficiencies are achieved if cells are plated the day before. However, adequate time should be allowed to allow the cells to recover from the passaging (generally >12 hours). Plate cells at a consistent density to minimize experimental variation. If transfection efficiencies are low or reduction occurs over time, thawing a new batch of cells or using cells with a lower passage number may improve the results.